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 Post subject: VFD PTW 6.5
PostPosted: Tue May 21, 2013 8:46 pm 

Joined: Thu Jun 02, 2011 4:47 am
Posts: 3
I am still unsure about how to model a VFD in PTW-
We are trying to model a Schneider - ATV71- ( please correct me if I am wrong)

There is NO contribution to the Line Side. - Correct ? as no bypass - Load side we should check the 100% and put in a % rating - what should that be, I assume it would be something? –Then we include an impedance. What impedance value should we input? 3% ?

Any help would be great,


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PostPosted: Mon May 27, 2013 5:12 pm 
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Joined: Tue Oct 26, 2010 9:08 am
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Location: North Carolina
Tim Smith wrote:
I am still unsure about how to model a VFD in PTW-
We are trying to model a Schneider - ATV71- ( please correct me if I am wrong)

There is NO contribution to the Line Side. - Correct ? as no bypass - Load side we should check the 100% and put in a % rating - what should that be, I assume it would be something? –Then we include an impedance. What impedance value should we input? 3% ?

Any help would be great,


Stop guessing. My experience is that you don't. You can use manufacturer data to determine available current on the output (usually 2x rated) which allows you to do either calculations manually on the output or to set it up in ptw as a voltage source and an impedance (a utility source) at best. If there is any better way then skm can tell you. On the input side it can theoretically output up to rated current (regen mode) but I haven't heard of modelling this. Most folks just set ip up as an impedance (value not important) and look at arc flash on the line side (looking up stream).


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PostPosted: Tue May 28, 2013 5:37 am 
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PaulEngr wrote:
Stop guessing. My experience is that you don't. You can use manufacturer data to determine available current on the output (usually 2x rated) which allows you to do either calculations manually on the output or to set it up in ptw as a voltage source and an impedance (a utility source) at best. If there is any better way then skm can tell you. On the input side it can theoretically output up to rated current (regen mode) but I haven't heard of modelling this. Most folks just set ip up as an impedance (value not important) and look at arc flash on the line side (looking up stream).


There are drives with automatic bypass switches, like those used to supply ventilation fans also used for smoke evacuation and other life safety or critical loads. If the drive or inverter fails there is a delay in the transfer to bypass, and they can be put into bypass manually and left in that state. You'll end up with an equivalent to a motor starter that would be worst case in the circuit as the motor will contribute to the fault current.

With regen drives, such as elevator motors, there is typically a limit of about 150% of the normal FLA of inverter rating for about 10 cycles. On page two of the SKM drive dialogue boxes for drives and UPS models you can enter these limits. Hope this helps.


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